This invention relates to communications systems and more specifically to direct sequence spread spectrum (DSSS) communications systems receivers.
Direct sequence spread spectrum communications system use wide over-the-air bandwidths. Conventional narrow-band signals may occupy the same frequencies used by the DSSS communications systems. To effectively recover the DSSS signal, the receiver in a DSSS system must excise the large narrow-band interfering signals from the receiver spectrum.
Various methods have been developed to excise large narrow-band signals using fast Fourier transforms (FFT). These methods result in circuitry that has high power consumption, occupies a large space, and has slow processing speed. For these reasons these methods are not easily implemented in small high-performance transceivers.
What is needed is a receiver employing a narrow-band signal excision function that effectively removes the interfering signals, has low power consumption, and is small in size.
A direct sequence spread spectrum (DSSS) communications receiver employing a narrow-band excision method is disclosed. The DSSS receiver comprises an antenna for receiving an input signal that may include a desired DSSS signal and one or more large narrow-band interfering signals. A down converter is connected to the antenna and includes an AGC controller for controlling the input signal level to the receiver with an AGC control signal to maintain a constant input signal level. The down converter also may include a mixer for down converting the input signal received from the AGC controller to an IF signal. An A/D converter may digitize the IF signal received from the mixer and a digital down converter may down convert the IF signal into an I/Q baseband signal. The A/D converter and the digital down converter may also be part of the down converter.
A detection channel connected to the digital down converter receives the I/Q baseband signal. The detection channel further comprises a spectral analysis function for performing a spectral analysis on a block of the I/Q baseband signal. A bin magnitude detector is connected to the spectral analysis function for detecting magnitudes of the I/Q baseband signal in frequency bins. An automatic gain control function is connected to the bin magnitude detector for generating the automatic gain control signal from the bin magnitude information in the frequency bins. A decision logic function connected to the bin magnitude detector compares the magnitudes of the I/Q baseband signal in the frequency bins to a threshold and determines corrupted frequency bin numbers containing one or more narrow-band interfering signals where the frequency bins contain signals exceeding the threshold.
A signal channel receives the I/Q baseband signal and further comprises frequency selectable band-reject filters to excise the one or more narrow-band interfering signals from the signal channel signal according to the corrupted frequency bin numbers. A demodulator subsequently demodulates the direct sequence spread spectrum signal in the signal channel.
It is an object of the present invention to provide a DSSS receiver that can excise one or more large interfering narrow-band signals.
It is an advantage of the present invention to provide a DSSS receiver that can excise one or more large interfering narrow-band signals using a simple magnitude spectral analysis and a bank of tunable band-reject filters.
It is a feature of the present invention to provide a DSSS receiver that can excise large one or more interfering narrow-band signals with circuitry that is small in size and has low power consumption.
These and other objects, features, and advantages are disclosed and claimed in the specification, figures, and claims of the present application.